Emulsions of organopolysiloxanes containing amino groups have been used heretofore as textile finishing agents. Good soft handle effects are obtained with the textiles treated with these agents. However, the amino-functional group --(CH.sub.2).sub.3 NHCH.sub.2 CH.sub.2 NH.sub.2 preferably used heretofore shows a strong tendency to thermal yellowing, a discoloration of the treated fibers which is accelerated by elevated temperatures.
A particularly effective reduction in thermal yellowing is achieved by reacting the amino-functional organopolysiloxanes with acylating agents, such as carboxylic acids and their anhydrides described in, for example, EP-A-349 753 and EP-A-349 754 (M. Ozake et al., published on Jan. 10, 1990 for Toray Silicone Co., Ltd., Japan), JP-A-57/101076 (K. Kodera et al., published on Jun. 23, 1982 for Nikka K.K. Co. Ltd., Japan) and EP-A-161 888 (T. J. Tangney et al., published on Nov. 21, 1985 for Dow Corning Corp., U.S.A.). Further acylating agents for reducing thermal yellowing are lactones, the use of which for modifying aminosilicone textile treatment agents is disclosed in, inter alia, EP-A-342 830 and EP-A-342 834 (S. E. Cray et al., published on May 5, 1989 for Dow Corning Ltd. Great Britain), carbonates, the use of which is disclosed in JP-A-90/47371 (S. Yokoyama et al., published Feb. 16, 1990 for Kyoeisha Yushi K.K. AG, Japan).
In all of the above processes the amino-functional organopolysiloxane is reacted in the form of an oil with the corresponding acylating agents. The viscosities of the oils, which are usually highly viscous, increase considerably as a result of the acylation. This leads to difficulties when emulsifying, since the viscosity impairs the mechanical miscibility and homogenization. In particular, the finished emulsions have relatively large particle sizes and broad particle size distributions. Therefore, the storage stability and shear stability of the emulsions are frequently unsatisfactory. When finishing textiles, emulsions of this type lead to non-uniform distribution of the silicone active compound on the textile substrate. Emulsions of this type can also lead to deposits on machine parts.
The acylating agents also reduce the soft handle effect of the treated textiles in the case of high degrees of acylation.
The reaction of amino-functional organopolysiloxanes with dialkyl oxalates and dialkyl pyrocarbonates as acylating agents in emulsions in order to reduce thermal yellowing and the use of the resulting emulsions as textile treatment agents is disclosed in U.S. Pat. No. 5,039,738 (A. M. Czech; issued on Aug. 13, 1991 for Union Carbide Corp., U.S.A.).
The dialkyl oxalates reduce thermal yellowing, but not to the same extent as, for example, acetic anhydride or dialkyl pyrocarbonates. In addition, because of their double reactivity towards amino groups ##STR1## dialkyl oxalates tend to crosslink amino-functional polysiloxanes. This crosslinking can have an adverse effect on the storage stability of emulsion formulations due to premature precipitation and when used can lead to undesired deposits of crosslinked silicone material on machine parts, such as squeezing rollers and the like.
Dialkyl pyrocarbonates do give a satisfactory reduction in thermal yellowing, but have the disadvantage that CO.sub.2 and alcohol are liberated during the reaction with amino-functional groups. However, the evolution of CO.sub.2 can lead to undesired foaming, and the formation of alcohol, such as methanol, which is hazardous on toxicological grounds. Moreover, dialkyl pyrocarbonates are either not available in industrial amounts or are very expensive.
Therefore, it is an object of the present invention to provide an emulsion containing acylated amino-functional organopolysiloxanes. Another object of the present invention is to provide a simple process for preparing acylated amino-functional organopolysiloxane emulsions. Still another object of the present invention is to provide an emulsion having good storage stability. A further object of the present invention is to provide a stable emulsion which may be used as a textile finishing agent or from which a textile finishing agent can be prepared from said emulsion. A further object of the present invention is to provide a textile finishing agent which provides the treated textiles with good soft handle properties and also a low tendency to thermal yellowing.